1. Field of the Invention
The present invention generally relates to a developing device. More specifically, the present invention relates to a developing device and an image forming device having the same.
2. Background Information
An image forming device, such as an electrophotographic copying machine, a printer, and the like, has a photosensitive drum (image carrier), and a developing device that provides developer to the photosensitive drum and makes the electrostatic latent image visible. The developing device generally has a casing that stores developer, a developing roller that is arranged opposite the photosensitive drum in the interior of the casing, and a mixing conveying screw (mixing conveying member) that mixes and conveys developer in the interior of the casing. The mixing conveying screw normally includes an axis portion, and a spiral (blade portion) that is formed in a spiral shape in the axial direction on the outer circumferential portion of the axis portion.
In this type of developing device, for example, in which storing toner is a one-component system developer, as toner is being mixed and conveyed by the mixing conveying screw, fluidity is lost due to wax or surface treating agent on the toner surface being gradually stripped away, and the like. Thus, the toner may attach and accumulate on the spiral of the mixing conveying screw. In this kind of situation, the mixing and conveying functions of the mixing conveying screw are being hindered.
Consequently, as a conventional developing device, there has been a device known which the shape of the spiral is improved so that toner will be less likely to attach thereon as shown in Japanese Patent Application Publication No. 2000-250299. The spiral shown in JP2000-250299 is designed to have both the mixing and the conveying functions.
In addition, there is a technology known for scraping off toner attached on a layer thickness control blade for controlling the thickness of toner layer on the developing roller as shown in Japanese Patent Application Publication No. 2001-249538.
Meanwhile, an electrophotographic image forming device further has a cleaning device for removing toner remaining on the surface of a photosensitive drum, around the photosensitive drum. The cleaning device is normally made of a cleaning blade that is in contact with the surface of the photosensitive drum, and a mixing conveying screw for mixing and conveying in one direction toner that is scraped off by the cleaning blade. In the cleaning device also, toner may attach to the mixing conveying screw, in the same manner as the developing device. Therefore, there is a device known with a film made of polyethylene terephthalate mounted on the mixing conveying screw to extend radially from the axis, to scrape off the toner.
As with the developing device in JP2000-250299, in the method for improving the shape of the spiral, the shape of the spiral becomes complicated, and even by improving the shape, it still cannot sufficiently prevent toner from attaching to it.
In addition, as with the above described cleaning device, in the technology adopting the resinous film, it is possible to scrape off toner attached on the spiral, but this hinders the function of conveying toner. Therefore, when adopting this technology in a developing device, functions that should be included in a developing device cannot be sufficiently secured.
In view of the above, it will be apparent to those skilled in the art from this disclosure that there exists a need for an improved developing device and an image forming device having the developing device. This invention addresses this need in the art as well as other needs, which will become apparent to those skilled in the art from this disclosure.